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Full text of "The Morphology And Evolution Of The Apes And Man"

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52            MOEPHOLOGY AND EVOLUTION
The Skull—The jaws exhibit prognathism, which varies in different genera, and is most marked in old animals. The skull differs from that in the Cebidae in the following ways:—
(1)  The frontal bone articulates with the squamous part of the temporal bone, thus separating the parietal and alisphenoid.
(2)  The tympanic bone   forms   a  tubular   external auditory meatus, and there is no bulla;  but the lower surface of the petrous temporal bone appears inflated in many cases.
(3)  The palate is long and narrow.
(4)  There are crests and ridges for the attachment of muscles.
The orifice of the naso-lachrymal duct is contained within the orbit as in the Cebidse; and the lachrymal and ethmoid bones are separated by the frontal and maxillary bones as in the Lemuroidea.
Teeth.—The incisor teeth have large crowns. The upper central incisors are larger than the upper lateral incisors, but the four lower incisors are nearly equal. The canine teeth may be very long, and there are diastemata between the upper canines and upper lateral incisors.
The upper premolar teeth are almost equal in size. They have three fangs and two cusps, of which the outer is larger than the inner. Of the lower premolars the first is large, pointed and caniniform, the outer cusp being very large and sharp; the second lower premolar has subequal external and internal cusps. The lower premolars have two roots.
The upper molar teeth have four cusps connected by